can someone tell me how they calculate gain/loss of DJIX on daily basis?

for example, today Dow Jones closed at 360 pts down, how was that calculated?

This link will show you:http://money.cnn.com/data/dow30/

The DOW consists of 30 large cap stocks. The average is computed from how well or poorly the stocks do. l believe they are adjusted according to number of shares outstanding times price per share or some such correction. Also, it is the DOW Industrials, no financials, etc. l believe Charles Dow, who set up the original, wanted a handle on railroads, steel and oil companies. Do not recall when it started but the DOW was less than 30 points to start as l recall.

The Dow Jones Industrial Average (DJIA) is comprised of thirty largest cap stocks. It is an index that shows how the large industrial r doing as whole.

It is based on the prices of:
Alcoa Inc.
Altria Group
American Express Co.
AIG.
Boeing Co.
Caterpillar Inc.
Citigroup Inc.
Coca-Cola Co.
DuPont Co.
Exxon Mobil Corp.
General Electric Co.
General Motors Corp.
Hewlett-Packard Co.
Home Depot
Honeywell International Inc.
Intel Corp.
International Business Machines Corp.
JP Morgan Chase & Co.
Johnson & Johnson
McDonald is Corp.
Merck & Co.
Microsoft Corp.
Minnesota Mining & Manufacturing Co.
Pfizer Co.
Procter & Gamble Co.
SBC Communications
United Technologies Corp.
Verizon.
Walt Disney Co.
Wal-Mart Stores Inc.

In the beginning, it was just the sum of the stock prices for each of them. However, with stock splits & time it has become more complicated.

Rather than copying & pasting the description, u can get the information here: http://investopedia.com/articles/02/082702.asp

Also, consider looking at the S&P500 & NSDAQ Industrial Averages which provided a different slice of how the market is doing.

they just average all the stocks in the dow

They took out AIG and put in Kraft l believe, since AIG was not doing so hot anymore. This happened just recently, and it happens whenever a certain company does poorly or goes bust. So take the DOW index with a grain of salt, it obviously will do better if you keep taking out the bad stocks, right?!